In the art and science of glassware manufacture, there are two basic methods currently employed for measuring rate of molten glass flow, such as in tons per day. The first method is to obtain a sample of glass as it exits the forehearth/feeder orifice, and weigh the sample. Although this technique provides an accurate measurement of glass flow, it causes loss of production due to the sampling. The second method is an indirect method, in that the glass flow is calculated by averaging batch charger material flow to the furnace. Although this method provides a fairly accurate measurement in a system in which the furnace feeds a single forehearth, it is ineffective for systems in which the furnace feeds two or more forehearths.
It is therefore a general object of the present invention to provide a method and apparatus for measuring molten glass flow through a forehearth that are accurate, that are implemented in the forehearth, and therefore can be readily employed in systems in which a furnace feeds more than one forehearth, and that do not require interruption of operation of the glassware forming system. Another and more specific object of the present invention is to provide a method and apparatus of the described character for both measuring and controlling rate of molten glass flow, in which glass flow adjustments are automatically implemented.
Apparatus for controlling rate of molten glass flow through a forehearth in accordance with one aspect of the presently preferred embodiment of the invention includes a flume disposed in the forehearth for restricting the width of the forehearth to glass flow, such that there is a difference in level of molten glass in the forehearth upstream and downstream of the flume. Sensors measure the level of molten glass upstream and downstream of the flume, and a controller is responsive to the sensors for determining rate of molten glass flow through the forehearth as a function of a difference in molten glass level between the sensors. In the preferred implementation of the invention, rate of glass flow through the forehearth is controlled as a function of the difference in glass level across the flume.
In the preferred implementation of the invention, the forehearth terminates in a spout having a lower opening for delivering molten glass. A flow control tube is disposed within the spout for movement toward and away from the spout opening to restrict or increase glass flow through the opening. Position of the flow control tube is controlled responsive to the controller for moving the tube with respect to the opening when rate of glass flow through the flume departs from a desired glass flow rate input by an operator. In glass flow systems that include multiple forehearths fed by a single furnace, the glass level measurement sensors and the flow control tubes in each forehearth operate independently of each other.
The flume is preferably disposed with respect to the direction of glass flow through the forehearth such that the depth of the forehearth and flume to glass flow remains constant, while the width to glass flow is the same upstream and downstream of the flume, while the flume includes a smooth transition upstream and downstream of a flume restriction to glass flow. This restriction preferably is coated with platinum or other corrosion-resistant material both to prevent pick-up of stones or particles in the glass eroded from the flume, and to maintain a constant flume cross-section to glass flow. The sensors in the preferred embodiment of the invention comprise contact-type sensors that are disposed above the forehearth, and are selectively lowered and brought into contact with the molten glass surface. Variable resistors or other suitable devices are coupled to the sensors for determining sensor position. The sensors preferably are zeroed prior to glass flow by lowering the sensors against a bottom wall surface of the forehearth. Knowing (or measuring) glass viscosity and temperature at the restriction area, glass flow can be accurately calculated based upon the difference in surface level upstream and downstream in the flume.